This invention relates to voltage-controlled oscillator (VCO) circuitry. More particularly, this invention relates to voltage-controlled oscillator circuitry operative to produce output signals in a wide range of frequencies.
VCO circuits produce clock signals of varying frequencies in response to variable input voltage signals. VCO circuits are used to generate clock signals in a wide range of circuit applications. VCO circuits are commonly used in transceiver and other communications applications to synchronize clock signals in circuits and devices that communicate with each other. VCO circuitry may, for example, be part of phase-locked loop (PLL) circuitry operative to synchronize the phase and/or frequency of multiple clock signals.
VCO circuits are generally designed to produce output clock signals with frequencies limited to a small range of frequencies. The range of frequencies a particular VCO circuit is operative to produce is typically limited by a tradeoff between the width of the VCO's frequency range and the phase noise at the output of the circuit. VCO circuits requiring minimal phase noise typically have restricted operating frequency ranges, while VCO circuits operative at a wide range of frequencies typically have higher phase noise.
In applications in which VCOs may be required to operate in a wide range of frequencies, such as in VCOs included on programmable logic devices (PLD) which may be required to support multiple different communications standards and frequencies, it may be difficult to provide VCO circuits with low phase noise characteristics over the required frequency range.
It is an objective of the present invention to provide VCO circuits with low phase noise characteristics over a wide range of operating frequencies. It is a further objective of the present invention to provide wide frequency-range VCO circuits that require minimal circuitry.